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Realizing Highly Efficient Solution-Processed Homojunction-Like Sky-Blue OLEDs by Using Thermally Activated Delayed Fluorescent Emitters Featuring an Aggregation-Induced Emission Property

Article excerpt is from:Kailong Wu, Zian Wang, Lisi Zhan, Cheng Zhong, Shaolong Gong, Guohua Xie, and Chuluo Yang
J. Phys. Chem. Lett. 2018, 9, 1547−1553

Two new blue emitters, i.e., bis-[2-(9,9-dimethyl-9,10-dihydroacridine)- phenyl]-sulfone (o-ACSO2) and bis-[3-(9,9-dimethyl-9,10-dihydroacridine)- phenyl]-sulfone (m-ACSO2), with reserved fine thermally activated delayed fluorescent (TADF) nature and simply tuned thermal and optoelectronic properties, were synthesized by isomer engineering. The meta-linking compound, i.e., m-ACSO2, obtains the highest photoluminescence quantum yield with a small singlet−triplet energy gap, a moderate delayed fluorescent lifetime, excellent solubility, and neat film homogeneity. Due to its unique aggregation-induced emission (AIE) character, neat film-based heterojunctionlike organic light-emitting diodes (OLEDs) are achievable. By inserting an excitonic inert exciton-blocking layer, the PN heterojunction-like emission accompanied by intefacial exciplex was shifted to a homojunction-like channel mainly from the AIE emitter itself, providing a new tactic to generate efficient blue color from neat films. The solution-processed nondoped sky-blue OLED employing m-ACSO2 as emitter with homojunction like emission achieved a maximum external quantum efficiency of 17.2%. The design strategies presented herein provide practical methods to construct efficient blue TADF dyes and realize high-performance blue TADF devices.